Enterocytozoon bieneusi grows within gut epithelial cells and causes chronic diarrhea in nearly 30% of AIDS patients (United States and Europe) with intestinal disorders. Since Enterocytozoon has not been established in an animal model or in tissue culture, drug testing has been limited to treatments of patients and with little success. The proposed investigation is to establish E. bieneusi in continuous culture in vivo and/or in vitro. The success of the project depends largely on the development of a protocol for isolating pure pellets of infective E. Bieneusi spores. This step is important for the studies on identifying the activation sequence for spore germination. Once the spore activation procedure is known, the probability is increased for a successful initiation of infections in vivo or in vitro. From a laboratory model drug testing can be done; also, more can be learned about how transmission takes place in humans. The present assumption is a vector or reservoir host may play a role in the maintenance of the pool of infective spores in the wild.